1. Field of the Invention
The invention relates to memories, and more particularly to memory access circuits.
2. Description of the Related Art
When an external circuit reads data stored in a specific memory cell, a bit line corresponding to the specific memory cell must first be charged to a high level. A word line corresponding to the specific memory cell is then enabled according to an address of the specific memory cell, and data stored in the specific memory cell is then loaded to the bit line. An output circuit then latches onto the data on the bit line and outputs the data to the external circuit. Thus, allowing the external circuit to obtain the data stored in the specific memory cell.
Meanwhile, because bit lines of the memory must be charged in advance (referred to as pre-charging), a pre-charge signal PRE is required to trigger the charge. In addition, because word lines of the memory must be enabled to select specific memory cells from the memory, an enable signal EN is required to trigger the selection. Pre-charging of the bit lines must be earlier than selecting of the word lines to ensure that voltages of the bit lines are raised to a target level before data is output from specific memory cells to the bit lines. FIG. 1 shows an ideal relationship between a pre-charging signal PRE and an enable signal EN. The rising time, T1, of the pre-charging signal T1 must be earlier than the rising time, T2, of the enable signal EN. In addition, the falling time, T3, of the pre-charge signal PRE must be later than the falling time, T4, of the enable signal EN. In other words, the duration D1 should cover the duration D2 to prevent memory access in error.